<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>呼吸灯</title>
    <style>
        div {
            box-sizing: border-box;
        }
        .content {
            background: #444;
            width: 300px;
            height: 500px;
            margin: auto;
        }
        .outer {
            height: 100%;
            width: 100%;
            border-radius: 50%;
            border: 10px solid #f4f4f4;
            margin: auto;
            padding: 20px;
            /* 引用动画 */
            animation-name: outer;
            animation-duration: 8s;
            /* 速度曲线 */
            animation-timing-function: linear;
            /* 次数 */
            animation-iteration-count: infinite;
        }
        .up {
            height: 300px;
            width: 300px;
            padding: 30px;
            border-bottom: 2px solid #f1f1f1;
            
            /* 引用内圆动画 */
            animation-name: inner;
            animation-duration: 8s;
            animation-timing-function: linear;
            animation-iteration-count: infinite;
        }
        .inner {
            height: 100%;
            width: 100%;
            border: 7px solid #f3f3f3;
            border-radius: 50%;
            
        }
        /* 定义外圆动画 */
        @keyframes outer {
            25% {
                padding: 30px;
            }
            50% {
                padding: 20px;
            }
            75% {
                padding: 20px;
            }
            100% {
                padding: 20px;
            }
        }

        /* 定义内圆动画 */
        @keyframes inner {
            25% {
                padding: 40px;
            }
            50% {
                padding: 30px;
            }
            75% {
                padding: 42px;
            }
            100% {
                padding: 30px;
            }
        }

    </style>
</head>
<body>
    <div class="content">
        <div class="up">
            <div class="outer">
                <div class="inner"></div>
            </div>
        </div>
        <div class="down"></div>
    </div>
</body>
</html>